The present invention relates to a milk fraction obtainable by acidification of micellar casein and separation from precipitated casein named acid soluble protein from micellar casein. It was found that the milk fraction and especially certain sub-fractions thereof are bioactive and promote GLP-1 release in vitro. Based on these results, acid soluble protein from micellar casein may be useful in the treatment and the prevention of diabetes type II, obesity and may further be added to formulas directed at other purposes addressing the gastro-intestinal tract.